3.4 Precompression of seal seat In order to ensure the tightness of pneumatic ball valve when the working pressure of medium is low, a certain preload specific pressure must be formed between the ball and seal seat. In the rigid seal seat, the reliability and service life of the pneumatic ball valve depend on the correct selection of the pre compression amount of the seal seat. The precompression shrinkage is insufficient to ensure the low pressure tightness of the pneumatic ball valve; Excessive pre compression will increase the friction torque between the ball and the seal seat, affecting the action performance of the pneumatic ball valve; And it may cause plastic deformation of the seal seat, leading to seal failure. For PTFE seal seat, its pre tightening specific pressure shall generally be 0.1PN and not less than 1.02MPa. The adjustment of the pre compression amount of the rigid seal seat is realized by changing the thickness of the seal adjusting gasket, and the machining error of the seal adjusting gasket will affect the adjustment effect; Reasonable assembly and adjustment is the key to obtain good sealing performance. In use, after the seal seat is worn, the automatic adjustment ability of preload specific pressure is very poor, so the service life of pneumatic ball valve with rigid seal seat structure is relatively short. One way to solve the problem is to use a seal seat with elastic elements. At this time, the acquisition and adjustment of the pre compression amount is no longer dependent on the sealing adjusting gasket, but is realized by the elastic element. The seal seat with elastic element can not only obtain the necessary pre compression, but also compensate the pre tightening pressure within the elastic deformation range of the elastic element. Therefore, the service life of the pneumatic ball valve is relatively long.

After cleaning, it is necessary to wait for the volatilization of the cleaning agent on the washed wall surface (it can be wiped with a silk cloth not soaked in the cleaning agent) for assembly, but it shall not be put aside for a long time, otherwise it will rust and be polluted by dust.
New parts shall also be cleaned before assembly.
Lubricate with grease. The lubricating grease shall be compatible with the metal materials, rubber parts, plastic parts and working media of the ball valve. When the working medium is gas, for example, special 221 grease can be used. Apply a thin layer of grease on the surface of the seal mounting groove, a thin layer of grease on the rubber seal, and a thin layer of grease on the sealing surface and friction surface of the valve stem.
During assembly, it is not allowed to have metal chips, fibers, grease (except those specified for use), dust and other impurities, foreign matters, etc. contaminating, adhering to or staying on the surface of parts or entering the cavity.